1. Field of the Invention
The present invention relates to an electron-beam generation device, and an image forming apparatus utilizing the electron-beam generation device.
2. Description of the Related Art
Two types of electron emitting devices, i.e., thermionic-cathode devices and cold-cathode devices, have been known. For example, surface-conduction-type emitting devices, field-emission-type (hereinafter abbreviated as xe2x80x9cFE-typexe2x80x9d) devices, and metal/insulator-metal-type (hereinafter abbreviated as xe2x80x9cMIM-typexe2x80x9d) emitting devices have been known as the cold-cathode-type devices.
For example, a device described in xe2x80x9cM. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965)xe2x80x9d or other devices to be described below have been known as the surface-conduction-type emitting devices.
The surface-conduction-type emitting devices utilize the phenomenon that electron emission occurs by causing a current to flow in a direction parallel to the surface of a small-area thin film formed on a substrate. In addition to the device described by M. I. Elinson which utilizes a SnO2 thin film, a device utilizing an Au thin film (G. Dittmer: xe2x80x9cThin Solid Filmsxe2x80x9d, 9, 317 (1972)), a device utilizing an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)), and a device utilizing a carbon thin film (H. Araki et al.: Shinku (J. Vac. Soc. Japan), vol. 26, no. 1, 22 (1983)) have been reported as the surface-conduction-type emitting devices.
FIG. 18 is a plan view of the above-described device by M. Hartwell et al., serving as a typical example of the configuration of a surface-conduction-type emitting device.
In FIG. 18, reference numeral 3001 represents a substrate. A conductive thin film 3004 is made of a metal oxide formed by sputtering.
As shown in FIG. 18, the conductive thin film 3004 is provided in the form of an H-shaped plane. By performing current-supply processing, called current-supply forming, on the conductive thin film 3004, an electron emitting portion 3005 is formed. In FIG. 18, a distance L is set to 0.5-1 mm, and a width W is set to 0.1 mm.
In order to facilitate understanding, the electron emitting portion 3005 is shown in the shape of a rectangle at the center of the conductive thin film 3004. However, this is a schematic diagram, which does not faithfully represent the position and the shape of the actual electron emitting portion.
In the above-described surface-conduction-type emitting devices inclusive of the device by M. Hartwell et al., the electron emitting portion 3005 is generally formed by performing current-supply processing called current-supply forming on the conductive thin film 3004 before performing electron emission.
That is, in the current-supply forming, current is supplied by applying a constant DC voltage or a DC voltage that increases at a very slow rate, such as about 1V/min, between both ends of the conductive thin film 3004, to locally destruct, deform or alter the conductive thin film 3004 in order to form the electron emitting portion 3005 that has a high electric resistance.
Cracks are generated at locally destructed, deformed or altered portions of the conductive thin film 3004.
When an appropriate voltage is applied to the conductive thin film 3004 after the current-supply forming, electron emission occurs at portions near the cracks.
For example, a device described in xe2x80x9cW. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956)xe2x80x9d, and a device described in xe2x80x9cC. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976)xe2x80x9d have been known as the FE-type devices.
FIG. 19 is a cross-sectional view of the above-described device by C. A. Spindt et al., serving as a typical example of the configuration of a FE-type device.
In FIG. 19, there are shown a substrate 3010, an emitter wire 3011 made of a conductive material, an emitter cone 3012, an insulating layer 3013, and a gate electrode 3104.
In this device, by applying an appropriate voltage between the emitter cone 3012 and the gate electrode 3014, field emission occurs from the distal end of the emitter cone 3012.
In another FE-type device, an emitter and a gate electrode are disposed on a substrate so as to be substantially parallel to the plane of the substrate, in contrast to the laminated structure shown in FIG. 19.
For example, a device described in xe2x80x9cC. A. Mead, xe2x80x9cOperation of tunnel-emission devicesxe2x80x9d, J. Appl. Phys., 32, 646 (1961)xe2x80x9d, and the like have been known as the MIM-type devices.
FIG. 20 is a cross-sectional view illustrating a typical example of the configuration of an MIM-type device. In FIG. 20, there are shown a substrate 3020, a lower electrode 3021 made of a metal, a thin insulating film having a thickness of about 100 angstroms, and an upper electrode 3023 made of a metal having a thickness of about 80-300 angstroms. In this MIM-type device, by applying an appropriate voltage between the upper electrode 3023 and the lower electrode 3021, electron emission occurs from the surface of the upper electrode 3023.
In the above-described cold-cathode devices, since electron emission can be obtained at a lower temperature than in the thermionic-cathode devices, heaters are unnecessary.
Accordingly, the cold-cathode devices have simpler structures than the thermionic-cathode devices, and therefore small devices can be formed. In addition, even if a large number of devices are disposed on a substrate at high density, problems, such as thermal melt of a substrate, and the like, will hardly arise. Furthermore, in contrast to a slow response speed of the thermionic-cathode devices operating by being heated, a high response speed is obtained for the cold-cathode devices.
Accordingly, applications of the cold-cathode devices are widely being studied. For example, the surface-conduction-type emitting devices are advantageous when forming a large number of devices on a large area, since they have simpler structures and can be more easily manufactured than other types of surface-conduction-type emitting devices.
Hence, as disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) No. 64-31332 (1989) by the assignee of the present application, methods for arranging and driving a large number of devices have been studied.
As for applications of the surface-conduction-type emitting devices, for example, image forming apparatuses, image recording apparatuses and charged beam sources are being studied.
Particularly, as for applications to image forming apparatuses, as disclosed, for example, in U.S. Pat. No. 5,066,883, and Japanese Patent Application Laid-Open (Kokai) Nos. 2-257551 (1990) and 4-28137 (1992) by the assignee of the present application, image forming apparatuses in which surface-conduction-type emitting devices and phosphors emitting light by collision with electrons are combined have been studied.
Image forming apparatuses combining surface-conduction-type emitting devices and phosphors are expected to have better properties than other conventional image forming apparatuses.
For example, these image forming apparatuses are superior to liquid-crystal displays which have recently been widely spread in that a backlight is not required and the angle of visibility is wide because these apparatuses emit light by themselves.
Methods for arranging and driving a large number of FE-type devices are disclosed, for example, in U.S. Pat. No. 4,904,895 by the assignee of the present application, and the like.
As an example of application of FE-type devices to an image forming apparatus, a flat display device reported by R. Mayer et al. (R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)) has been known.
An example of application of a large number of MIM-type devices to an image forming apparatus is disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) No. 3-55738 (1991) by the assignee of the present application.
From among image forming apparatuses using the above-described electron emitting devices, thin flat-surface-type display devices are expected to replace CRT (cathode-ray tube)-type display devices because of their smaller space and lighter weight.
Flat-surface-type display panel units in which an electron-source substrate having such electron emitting devices arranged in the form of a matrix formed thereon is accommodated within an airtight container have been proposed. The inside of the airtight container is maintained at a vacuum equal to or less than about 10xe2x88x924 Pa.
Japanese Patent Application Laid-Open (Kokai) No. 5-6748 (1993) discloses a configuration in which in order to reduce the weight of a flat-surface-type CRT, a portion of an accommodating container is made of metal and the metal portion is provided with a ground potential. Also disclosed are a configuration in which a creeping distance is increased by forming protrusions and recesses on the inner surface of screen glass in order to prevent creeping discharge, and a configuration in which a film for preventing secondary electron emission is formed.
FIG. 21 is a schematic diagram in which a display panel is seen from a horizontal direction of an image display surface.
As described above, since the inside of this airtight container must be maintained at a vacuum equal to or less than about 10xe2x88x924 Pa, it is necessary to provide means for maintaining a degree of vacuum.
Hence, conventionally, as shown in FIG. 21, a Ba-evaporation-type getter member 70 is disposed outside of an image region together with a getter supporting member 71. The degree of vacuum is maintained by evaporating Ba according to high-frequency heating or the like after sealing the vacuum container, to form a getter film.
In FIG. 21, there are shown a rear plate 1 also operating as an electron-source substrate, an electron-source region 2, a supporting frame 10, a faceplate 20, and an image forming member 3 consisting of a phosphor film and a metal film (for example Al) called a metal back.
In order to accelerate electrons emitted from an electron source, a high voltage (Va) of about several hundreds to several thousands of volts is applied between the electron-source region 2 and the image forming member 3.
The luminance of the image forming apparatus greatly depends on the voltage Va. Accordingly, in order to further increase the luminance, it is necessary to increase the voltage Va.
In accordance with a larger voltage Va, the electric field around the getter member 70 and the getter supporting member 71 outside of the image region also increases. As a result, discharge at portions whose shapes tend to cause concentration of the electric field, such as edge portions of the getter member 70 and the getter supporting member 71, and the boundary between the getter supporting member 71 and the rear plate 1, causes a problem.
In another approach, in order to maintain the atmospheric pressure, as shown in FIG. 22, a structural supporting member (spacer) 13 consisting of a relatively thin glass plate is provided between a rear plate 1 and a faceplate 20 together with a spacer fixing member 14 disposed outside of an image region. FIG. 22 is a schematic diagram illustrating a spacer supporting portion of a conventional electron-beam generation device.
Since the surface of the spacer 13 is exposed to a high electric field, creeping discharge at this surface is a conventional problem.
In order to solve this problem, there have been proposals of removing charges by causing a small current to flow along the surface of the spacer (Japanese Patent Application Laid-Open (Kokai) Nos. 57-118355 (1982) and 61-124031 (1986)). In these proposals, a small current is caused to flow along the surface of the spacer by forming a high-resistance thin film on the surface of the insulating spacer, to reduce charges on the surface and increase the breakdown voltage on the surface.
However, the studies made by the inventors of the present invention have cleared that even if the above-described antistatic film is also provided on the spacer fixing member, discharge at the spacer fixing member cannot be completely prevented depending on conditions of application of a high voltage.
It is considered that this is due to disturbance in the distribution of the potential caused by complexity of the shape of the spacer fixing member, the shape effect (edges and projections), and concentration of the electric field at, for example, a connection portion between the spacer and the spacer fixing member.
Accordingly, as shown in FIG. 23, when there is a structure outside of an image region, discharge at the structure is prevented by adopting a configuration in which a low-resistance conductive member 80 is formed on the inner surface of the faceplate 20 so that a portion of the low-resistance conductive member 80 is closer to the image region than the structure, and is maintained at a ground potential. FIG. 23 is a schematic diagram illustrating a getter portion of a conventional electron-beam generation device.
However, when reducing the distance between the conductive member maintained at a cathode potential and the image region in order to reduce the size of the image forming apparatus, creeping discharge between the conductive member and the image region sometimes causes a problem.
Even at a portion outside of the image region where a structure, such as the getter supporting member or the spacer supporting member described above, is not present, when reducing the distance between the supporting frame 10 and the image region, creeping discharge at the inner surface of the supporting frame 10 sometimes causes a problem.
The above-described discharge abruptly occurs during image display to disturb the displayed image and greatly degrade the electron source near the discharging portion, resulting in incapability of normally displaying the subsequent image.
It is an object of the present invention to provide an electron-beam generation device and an image forming apparatus for obtaining an excellent displayed image by suppressing undesirable discharge.
According to one aspect, the present invention which achieves the above-described object relates to an electron-beam generation device including an electron-source substrate having electron emitting devices, and a facing substrate disposed so as to face the electron-source substrate. An anode-potential regulating region which a potential to accelerate electrons emitted from the electron emitting devices is applied on, a conductive member, disposed around the anode-potential regulating region with a predetermined interval therewith, which a predetermined potential is applied on, a resistive film contacting the anode-potential regulating region and the conductive member, and a protrusion, positioned between the anode-potential regulating region and the conductive member, which is convex with respect to the electron-source substrate are provided on the facing substrate.
It is preferable that a height of the protrusion is at least 1 xcexcm.
It is preferable that the protrusion is disposed so as to surround at least three sides of the anode-potential regulating member.
It is preferable that the electron-source generation device further includes a spacer provided between the electron-source substrate and the facing substrate so as to maintain an interval between the electron-source substrate and the facing substrate. At least part of the spacer and a member for fixing the spacer is present outside of the anode-potential regulating region. The protrusion is formed at a portion other than a portion where the spacer or the member for fixing the spacer is formed.
According to another aspect, the present invention which achieves the above-described object relates to an electron-beam generation device including an electron-source substrate having electron emitting devices, and a facing substrate disposed so as to face the electron-source substrate. An anode-potential regulating region which a potential to accelerate electrons emitted from the electron emitting devices is applied on, a conductive member, disposed around the anode-potential regulating region with a predetermined interval therewith, which a predetermined potential is applied on, a resistive film contacting the anode-potential regulating region and the conductive member, and a recess, positioned between the anode-potential regulating region and the conductive member, which is concave with respect to the electron-source substrate is provided on the facing substrate.
It is preferable that the recess is disposed so as to surround at least three sides of the anode-potential regulating member.
It is preferable that the electron-source generation device further includes a spacer provided between the electron-source substrate and the facing substrate so as to maintain an interval between the electron-source substrate and the facing substrate. At least part of the spacer and a member for fixing the spacer is present outside of the anode-potential regulating region. The recess is formed at a portion other than a portion where the spacer or the member for fixing the spacer is formed.
According to still another aspect, the present invention which achieves the above-described object relates to an electron-beam generation device including an electron-source substrate having electron emitting devices, and a facing substrate disposed so as to face the electron-source substrate. An anode-potential regulating region which a potential to accelerate electrons emitted from the electron emitting devices is applied on, a conductive member, disposed around the anode-potential regulating region with a predetermined interval therewith, which a predetermined potential is applied on, a resistive film contacting the anode-potential regulating region and the conductive member, and protrusions and recesses positioned between the anode-potential regulating region and the conductive member are provided on the facing substrate.
It is preferable that the protrusions and recesses are disposed so as to surround at least three sides of the anode-potential regulating member.
It is preferable that the electron-source generation device further includes a spacer provided between the electron-source substrate and the facing substrate so as to maintain an interval between the electron-source substrate and the facing substrate. At least part of the spacer and a member for fixing the spacer is present outside of the anode-potential regulating region. The protrusions and recesses are formed at a portion other than a portion where the spacer or the member for fixing the spacer is formed.
According to yet another aspect, the present invention which achieves the above-described object relates to an electron-beam generation device including an electron-source substrate having electron emitting devices, and a facing substrate disposed so as to face the electron-source substrate. An anode-potential regulating region which a potential to accelerate electrons emitted from the electron emitting devices is applied on, and a conductive member, disposed around the anode-potential regulating region with a predetermined interval therewith, which a predetermined potential is applied on are provided on a same surface of the facing substrate facing the electron-source substrate. A multiple-scattering suppression structure for suppressing multiple scattering of secondary electrons generated by electrons emitted from the conductive member is disposed between the anode-potential regulating region and the conductive member on the same surface.
In the above-described inventions, it is preferable that the conductive member is disposed so as to completely surround the anode-potential regulating region.
In the above-described inventions, it is preferable that the resistive film causes a small current to flow between the anode-potential regulating region and the conductive member, and that a sheet resistance of the resistive film is within a range equal to or more than 1xc3x97107 xcexa9/xe2x96xa1 and equal to or less than 1xc3x971014 xcexa9/xe2x96xa1.
In the above-described inventions, it is preferable that each of the electron emitting devices is a cold-cathode device, that each of the electron emitting devices has a conductive film including an electron emitting portion between electrodes, and that each of the electron emitting devices is a surface-conduction-type electron emitting device.
In the above-described inventions, it is preferable that a voltage applied between the anode-potential regulating region and electrodes on a surface of the electron-source substrate having the electron emitting devices is at least 3 kV.
In the above-described inventions, it is preferable that a potential lower than the anode potential is applied on the conductive member. It is also preferable that a cathode potential is applied on the conductive member.
In the above-described inventions, it is preferable that a ground potential is applied on the conductive member.
This application also includes inventions of image forming apparatuses at each of which phosphors emitting light by electrons emitted from the electron emitting devices are added to each of the electron-beam generation devices of the above-described inventions.
The foregoing and other objects, advantages and features of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.